Merge branch 'stable-3.0' into stable-3.1

* stable-3.0:
  Use Gerrit 3.0.8 in Dockerfile
  Use Gerrit 2.16.17 in Dockerfile
  Dockerfile: Add delete-project plugin to instances
  e2e-tests: Adapt json filename constant to new name
  e2e-tests: Introduce a CloneUsingHAGerrit2 scenario

Change-Id: I799eb9feb5676da9399cf7f24b5cd51a1cb89e4d